Generally speaking, the hardness, or firmness, of a conventional bed comprising a mattress supported by a base is determined by the choice of materials made during the construction of each of the mattress and the base. Consequently, beds are available in which the firmness can vary at different points within a particular bed, and in which the overall firmness varies between separate beds. However, the only choice of firmness which a user can make with such a conventional bed or mattress is made when the bed or mattress is purchased. Thereafter, the user has little further choice, other than to replace the item. Choice on purchase is apparently simple, and is usually a matter of trial and error. Generally, the choice is made by sitting or lying briefly on the mattress, for example in a bedding store. This is not an adequate or very reliable test method. A further significant problem can arise if either a need is encountered to change the firmness of an existing bed (either temporarily or permanently), or if two persons using a double bed require radically different firmnesses. For example, one person may require a very firm support for orthopaedic reasons, whilst the other may find such a level of firmness. uncomfortable to the point that sleep is not possible.
There are also problems of deflection transmission sideways across a bed, especially if one user is of significantly different weight to the other.
This invention seeks to mitigate and to overcome these problems by providing a mattress system in which the firmness can be chosen at will, even on a daily basis, and in which different firmness for each of two users is practical. This invention also seeks to provide a mattress for a single person in which the hardness can be changed, either temporarily or permanently, in response to a perceived need.
Additionally, a mattress according to this invention can be maintained at a given level of firmness on an on-going basis over a period of time. Consequently, such a mattress is not subject to the loss of firmness encountered with a conventional mattress after an extended period of use. Further, this invention seeks to provide a mattress for two people which permits each person to select a desired level of firmness, and also to be able to change each persons' part of the mattress, either permanently or temporarily, in response to a perceived need. Furthermore, this aspect of the invention also seeks to provide a mattress for two people in which the top surface is always at the same height across its full width, regardless of the firmness selected, in which there is a smooth transition from one part of the mattress to the other, and also no significant intervening gap.
It is known that by using various combinations of the currently available elastomeric foam materials (in the past, these were either natural or synthetic rubber; in more modern practice, polyurethanes are used), a level of variation of firmness can be obtained. Thus Hood, in U.S. Pat. No. 3,118,153 describes an upholstery construction wherein corners are strengthened by using two layers of soft foam with a layer of harder foam in between them. Boyles, U.S. Pat. No. 3,534,417 applies similar concepts to a mattress, to provide some level of choice. A different level of firmness is obtained by turning over either the whole mattress, or an intermediate portion thereof extending across the full width of the bed. All of the mattress portions are enclosed within a common casing. Whilst this does give a flat sleeping surface, only a very limited number of choices of firmness are provided.
Johnson, U.S. Pat. No. 2,121,339 describes a more complicated system. The mattress consists of two layers of foam of differing firmness with a hard board layer in between them. The firmness is changed by reversing the elements making up the mattress. Thus, although a constant thickness results, few choices of firmness are allowed. For a double bed, it appears that the whole surface would have to have the same firmness. A similar mattress utilizing two layers of dissimilar foam is described by Slemmons, U.S. Pat. No. 3,110,442. In this mattress, two stacked resilient members are used of different firmness, with a provision to insert firming slats, either at predetermined points, or more or less anywhere, across the width of the mattress. A mattress using a plurality of encased foam pad elements is described by Betten-Zellekens in German 1,940,763. This mattress is somewhat similar to that described by Slemmons, in that a stiff, preferably plywood, panel is included into the stack. Thus, although a plurality of foam elements is used, the only way to adjust the firmness is to reposition the plywood insert within the stack
It has now been realized that a mattress can be provided which both provides a uniform and constant sleeping surface height at substantially the same level as a conventional bed, and yet which provides the, or each, user with a high degree of choice of firmness.